Apostasy in Islam (ردة, or ارتداد, ) is commonly defined as the abandonment of Islam by a Muslim, in thought, word, or through deed. It includes not only explicit renunciations of the Islamic faith by converting to another religion or abandoning religion, but also blasphemy or heresy by those who consider themselves Muslims, through any action or utterance which implies unbelief, including those who deny a "fundamental tenet or creed" of Islam, (such as suggesting jinn are not real).
An apostate from Islam is known as a murtād (مرتدّ).
While classical Islamic jurisprudence calls for the death penalty of those who refuse to repent of apostasy from Islam, what statements or acts qualify as apostacy and whether and how they should be punished, are disputed among Islamic scholars, while punishment is strongly opposed by Muslim, Non-Muslim and secular supporters of the universal human right to freedom of faith.
Until the late 19th century, the majority of Sunni and Shia jurists held the view that for adult men, apostasy from Islam was a crime as well as a sin, punishable by the death penalty, but with a number of options for leniency (such as a waiting period to allow time for repentance; enforcement only in cases involving politics,)
depending on the era, the legal standards and the school of law. In the late 19th century, the use of legal criminal penalties for apostasy fell into disuse, although civil penalties were still applied.
As of 2021, there were ten Muslim-majority countries where apostasy from Islam was punishable by death, but legal executions are rare. Most punishment is extra-judicial/vigilante, and most executions are perpetrated by jihadist and "takfiri" insurgents (al-Qaeda, ISIL/ISIS/IS/Daesh, the GIA, and the Taliban).
Another thirteen countries have penal or civil penalties for apostates - such as imprisonment, the annulment of their marriages, the loss of their rights of inheritance and the loss of custody of their children.